The process of hydrostatically testing a length of pipe generally comprises fitting sealing devices into or around the ends of the pipe to be tested, admitting hydrostatic test fluid through an opening in one of the sealing devices, filling the pipe with hydrostatic test fluid, increasing the hydrostatic pressure on the test fluid to a predetermined value, checking the pipe for any cracks or structural irregularities through which the test fluid may be leaking under pressure, reducing the level of hydrostatic fluid pressure on the test fluid in the pipe after the test has been completed and removing the hydrostatic test fluid from the pipe.
While many types of hydrostatic pipe testing apparatus exist in the prior art, few of these are designed to safely and effectively test large diameter pipe such as casing. The basic problem to be solved in the hydrostatic testing of large diameter pipe is that the fluid pressures to which the interior of the pipe must be subjected exert great forces on the sealing devices which are used to seal the ends of the pipe. For example, the force on a sealing device which seals the end of a thirteen inch (13") diameter casing is approximately 400,000 lbs. when the test pressure is approximately 3,000 lbs. per square inch.
Although the invention is capable of testing both threaded pipe and non-threaded pipe, the description of the invention will be primarily directed to the mode of operation for testing threaded pipe. A threaded test plug is the sealing device most commonly used to seal threaded pipe. Because threaded pipe has both male and female ends, two types of threaded plugs are required to seal a threaded pipe. Specifically, a female threaded test plug must be provided to thread onto the male end of the threaded pipe and a male threaded test plug must be provided to thread into the female end of threaded pipe.
The magnitude of the forces involved in testing large diameter pipe may cause a threaded test plug to be blown from the end of the pipe if there is a structural failure of the threads of the pipe onto which the test plug is threaded. A test plug may also be blown from the end of the pipe if there is a structural failure of the threads of the test plug or if the test plug is improperly threaded into or onto the end of the pipe to be tested.
Because of the large forces involved it has generally been conceded that such a high pressure failure could not be prevented. Accordingly, prior art attempts to solve the problem have been directed toward catching the test plugs once they have been blown from the end of the pipe. In contradistinction, the present invention comprises an apparatus and method for providing sufficient restraining force to prevent the test plugs from being suddenly blown from the ends of the pipe during a high pressure test failure.
Of course, very large or massive backstops or retaining walls could be constructed between which the pipe could be wedged in order to securely hold the test plugs on or within the ends of the pipe. The backstops or retaining walls would be designed to have sufficient strength to withstand the enormous forces acting on the test plugs. One disadvantage of such a design is that the pipe testing apparatus would not be easily portable due to the mass and size of the necessary backstops or retaining walls. The design of the present invention, however, provides a relatively lighweight and easily portable structure capable of counteracting the large forces tending to push the test plugs out of the end of the pipe being tested.